1. Field of the Invention
The present invention relates to an antenna system, and more particularly, to an antenna system for terrestrial broadcasting designed to receive a television (TV) broadcast signal and deliver the television (TV) broadcast signal.
2. Description of the Related Art
While a National Television Systems Committee (NTSC) standard is an analog TV broadcast standard used today in North America, an Advanced Television Systems Committee (ATSC) standard is a digital TV broadcast standard. Broadcasts adopting a new technology called data in NTSC video (dNTSC) to embed a digital signal into the existing NTSC TV frequency range are being made over a Very High Frequency-High (VHF-H) band. An indoor or outdoor antenna is needed to receive the VHF-H broadcasts. An indoor antenna is more advantageous than an outdoor antenna in many aspects since the antenna must be connected to a digital set-top box to receive digital broadcasts
FIG. 1 is an exemplary diagram showing the spectrum of frequencies within a VHF-H band, over which a dNTSC technique is applied.
Here, double sideband (DSB) modulation is used to mix an analog broadcast signal 100 and a digital broadcast signal 110 into a carrier. While a NTSC format allows a carrier having a frequency fvisc to carry the analog broadcast signal 100 having a frequency range of fc1 to fch, a dNTSC format is used to additionally carry the digital broadcast signal 110, that is, to transmit a dNTSC data signal outside the frequency range of the analog broadcast signal 100.
FIG. 2 is a table listing frequencies of the respective signals shown in FIG. 1 for VHF channels 7 through 13. The frequency of the carrier ranges from about 170 to about 220 megahertz (MHz) on the channels 7 through 13. Regardless of the channel, the analog broadcast signal 100 has a bandwidth of 0.1 MHz while the dNTSC 110 has a bandwidth of 0.76 MHz.
However, an indoor antenna for receiving a VHF-H signal including a digital broadcast signal is subject to space restrictions. Due to the space restrictions, it is difficult to determine the size of an antenna that varies according to a frequency band and realizes a dipole antenna. Thus, it is highly desirable to have an indoor antenna having a desired electrical length while occupying a small space to enable users to watch television broadcasts on Ultra High Frequency (UHF) band as well as VHF-H band.
Furthermore, a broadcast signal needs to be amplified in an antenna to improve its signal to noise ratio (SNR), since a higher SNR is achieved when the signal is amplified in the antenna before being sent to the next stage. In the case of a dipole antenna, the antenna must be designed to solve problems arising between a balance circuit and an unbalance circuit for signal amplification.